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Патент USA US2106734

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Feb.-_l, 1938.
H. A. GQLLMAR
2,106,734 ì
GAS PURIFICATION PROCESS
Filed Feb. 27, 1935
>&2/ ATTORNEY.
2,106,734
Patented Feb. 1, 1938
UNITED VSTATES PATENT OFFICE
2,106,734
GAS PURIFICATION PROCESS `
Herbert A. Gollmar, Union Township, N. J., as
signor, by mesne assignments, to Koppers Com
pany, a corporation of Delaware
Application February 27, 1935, Serial No. 8,501
15 Claims.
This invention relates in general to a process
of purifying coal-gas or the like of acidic gases
by means of ammonia with separation of the am
monia and acidic gases into their chemical
.5 classes, and more particularly to a method which
permits of the production of substantially pure
hydrogen sulphide from such gaseous mixtures
(o1. 23-3)
tion gases being carried forward to the saturator,
and that ammonia which is used for the purpose
of fortification being retained in a separate or
secondary system where it is continuously re
used for the removal of the acidic gases.
CFI
,
My invention relates in particular to a method
whereby ammonium salts of the acidic gases such
as are evolved from coal during its carbonization.
as are formed in the scrubbing solution during
bonization period is composed not only of chemi
sulphuric acid or production of elemental sulphur
substantial amounts of hydrogen sulphide, hy
drogen cyanide, carbon dioxide and ammonia,
may be returned to the- scrubbing system for
further eiîective use in removal of more of the
By “acidic gases” asl hereinafter referred to I ‘ the washing operation may be subsequently sub
stantially separated into acidic gases and am- 10
i 1U mean those gases which in solution in water are
acid in reaction but which are easily volatilized monia, following which separation the acidic
gases consisting principally of hydrogen sul
unchanged upon heating.
phide can be burned for the manufacture of
The gaseous mixture given off during the car
15 cally neutral derivatives of carbon but also of ~ as by the method of Claus, whereas the ammonia 15
and the substantially complete removal of these
last named compounds is highly desirable before
¿u the introduction of the gases of carbonization
into a distribution system or before it is used as
a fuel. If these chemical -entities are present in
the gas in proper proportions, they can be used
for their mutual extraction.
_ «_»5
.
In the prior art various methods have bee
tried to accomplish this end but they have proven
economically unsatisfactory because of the am
monia losses experienced, the extensive equip
ment required in the various applications and
3;; the disposal of excessive amounts of waste liquor.
In my present invention, I provide a means
aforementioned acidic gases. This separation is
accomplished by first heating the fouled scrub
bing solution from the absorber, (i. e. the solution 20
containing ammonium sulphide, carbonate and
cyanide) at optimum temperatures and in such
manner as to remove the absorbed acidic gases
from the same, whereupon the liberated gases
consisting of steam, -some ammonia and princi- 25
pally hydrogen sulphideI are separated by means
of. a selective absorbent which has a greater
añinity for ammonia than it has for the acidic.
gases. The ammonia can then be substantially
completely retained in the selective absorbent 30
and the acidic gases pass out of the system to be
whereby substantially all hydrogen sulphide can - made optional disposition of.- The selective ab
be removed from such gases by means of am
monia without serious material loss of the latter,
3:, avoiding as well other objections that have
v arisen in the prior art attendant upon any appli
cation
That of
a simple
this idea
washing
to theofpractice.
a gaseous admixture
`
containing ammonia and acidic gases such as
4:) HCN, CO2 and HzS with water or ammonia liquor
in the manner long established in the art, will
serve to remove not only the ammonia but the
acidic gases as well, is a fact long known in the
practice. Whether a complete or only partial
4.3 removal of these acidic constituents is effected,
depends upon the ratio of ammonia to acidic
compoundsV in the gas treated and in most cases
where a complete removal’of- the latter is de
sired, the ammonia content must be substantially
50 increased above that normally present; but as
hereinafter described the ammonia used for this
sorbent now carrying absorbed ammonia may be
next subjected to a distillation process, thus
liberating the absorbed ammonia which may be 35
returned to the untreated gases produced in the
carbonization process, to be again used for- the
removal of more of the acidic gases. The selec
tive absorbent having been deprived of its arn
monia content may then again ~be used for the 40
separation of more ammonia from its admixture
with the acidic gases. The_discovery of this ap
plication of preferential or selective absorbents
and their method of use is among the novel parts
ofv this invention. 'I'he invention has for further 45
objects -such other improvements and such other
operative advantages or results as may be found
to obtain in the processes or apparatus herein
after described or claimed.
-
In the accompanying drawing forming a parir 50_
of this speciñcation and showing >for purposes of
.exempliflcation, a preferred form and manner in
purpose in my invention is continuously re
which the invention may be embodied and prac
covered and returned to the gas scrubbing sys
tem in such manner as to- permit of the normal ticed, but without limiting the claimed invention
speciñcally to such illustrative instance or in- 55
5.', quantity of ammonia present in the carboniza
2
2,106,734
'
stances, the- single figure shows diagrammatically
that passes into the selective absorber and as
in elevation the ilow of liquids and gases in their _ sists 'in maintaining the desired concentration
preferred sequence of operation for the practice
of the invention.
` of the selective absorbent and also serves to only `
moderately cool the vapors to a temperature still
~
The gases evolved duringvthe carbonizatlon of . high enough and at which the selective absorb
the coal in the coke-oven l rise through the as
ent solution will not absorb more than- a minor ..
l cension pipe 2 and passinto the collecting main amount of yI-InS while simultaneously preferen
I where they are sprayed with gas liquor which is tially absorbing the ammonia. Such dephlegma
pumped from the bottoni- of the primary’ cooler tion thus both' effects condensation that wouldl
10 -4 by means of pump 5 through line 8, in which otherwise take place in- the lselective absorbent
operation the hot gases are somewhat cooled and
a portion of the tar-fog is condensed. 'I‘he gas
liquor and condensed tar overflow through 1
into pitch-trap I from which they are sent toy
storage. 'I‘he distillation gases simultaneously
pass through 'I and pass from pitch-trap 8
through pipe 9 into- the bottom of primary cooler
I, where they meet a counter-current ilow of
water, gas liquor, or combination of both. which
20 enters the cooler 4 by means of spray-header It,
and which operative step further cools the gases,
and at the same time removes some additional
tar as well as some ammonia and aportion of
the acidic gases. >The ammoniacal liquor collects
from the
cooler, through downcomer Il to lthe ilnal tar
25 in the base ofpl while the gas'
extractor I2 and to exhauster Il. Prom the base
of l the ammoniacal liquor
by means of
line il to cooling coils Il. where its temperature
is reduced by indirect contact with cooling wa
ter distributed from 23, whence it flows through
line 24 to the spray-header atop absorber 2B,
where the gas liquor ’is again brought in con
tact in counter-current ilow with the gas pumped
35 into the bottom of the absorber 2l by the ex
hauster Il." This step atl’drds the ammonia
bearing gas liquor` passing through 24 opportu
nity to effect further removal of the acidic gases
from the gasœ of carbonization passing through
40 the absorber. It is evident from the prior art
that the extent of removal effected depends upon
the ammoniacal concentration of said gas liquor
and its rate of circulation. as well as the con
centration of acidic gases in the gases of car
45 bonimtion and the rate of ilow of the latter
through the absorber 2l. If complete removal
from the vapors rising from the desulphurizing
stage which condensation would lead to undue
dilution of the selective absorbent and also as
sists in minimizing the rate at which the selec
tive absorbent solution must4 be circulated and
bears `directly on the heat economies oi' the proc
ess since it reduces the volume of steam that
must be later used in the deammoniation stage
to expel the ammonia and maintain the desired
concentration of .the selective absorbent solu 20v
tion.
`
.
v
„
The gas liquor now substantially freed of its
acidic gases passes out of the desulphurizer into
pipe 36 and by proper adjustment of valves i1
and i8 can be sent either wholly or partially to
the ammonia still 20 to be freed of the remain
der of its ammonia content and be eliminated
from the system as still waste, or may be "passed
through heat exchanger i0, cooling coils I5, pipe
24, into absorber 25 where its ammonia content
will still be of service for the removal of more
acidic gases from the untreated gases produced
by the carbonization'of coal in the oven I.
The dephlegmation, -by dephlegmator 34„l ls so
limited that at the resulting moderately reduced I
temperature the selective absorbent solution in
35 will absorb only a minor portion of the hy-l
drogen sulphide while preferentially absorbing
substantially all of the residual ammonia from
the mixture.
,
'
through line I'l. 'I'he selective absorbent solu 45
tion having a high preferential absorptive ailin
4 of the acidic gasœ is desired, a higher-concen
ity for ammonia removes the same from the gas
tration of ammonia in the gas liquor may be re
quired than otherwise. The coal gas now par
50 tially freed or completeb purlñed of acidic gases
eous mixture passing through the selective ab
sorber and allows a substantial part of the _acidic
gases to pass out of the system at the outlet 30,
from which point they can be made use of as
.` ~ passes to reheater 2l and on into saturator 21
where its ammonia content is» removed by sul
preferred.
phuric acidin the customary manner; then
’I‘he selective absorbent, which now contains
absorbed ammonia and relatively small amounts
of acidic gases, passes from the selective absorb
passes to an acid separator“ and into the iinal
55 cooler 2t.
v
The now fouled gas liquor collects at the bot
tom of the absorber 2| and by pump 2l
:.~~-
to line Il through heat exchanger it into line
32 and discharges into the desulphuriner 33. In
the desulphuriaer the fouled gas liquor flows over
trays equipped withy bubble-caps >and through
which the hot- ammonia vapors from the am
monia still 2l carried by pipe 22 pass in coun
ter-current manner. heating the fouled liquor,
thus> causing it to liberate a substantial propor
tion o_f the absorbed acidic gases. The elimina
tion of these acidic gases from the fouled solu
tionis accompanied by some ammonia.
~
'Ihehotmixedgasesthenpassupwardover
70 a dephlegmator Il where they are somewhat
cooled and a portion of their water vapor is con
densed out which returns to the desulphurizer,
whereas the ammonia and acidic gases pass on
into the selective absorber 3l. 'nie dephlegrna
torthusservestoreducetheamountofwater
r
. 40.
The admixed ammonia and acidic gases upon
entering the selective absorber 'II pass through
bubble-cap trays and are brought into counter
current contact with the selective absorbent
-
er 35 through pipe 38 and is sent. by pump 4l
through the heat exchanger 4| to .the upper `sec
tion 42a of the deammoniator >42. In the deam
>moniator the selective absorbent is stripped of
the ammonia absorbed in the selective absorber.
This may be accomplished in a two-stage heat
treatment as shown for purposes of exemplinca
tion in the accompanying drawing, but the' in
vention is not limited in all its applications ‘to
this particular application of the principle in
volved. '
l
In 42a the ammonia-laden selective absorbent
ñows over the trays provided with bubble-,caps
as illustrated and iis heated with indirect steam
for the removal oi' the bulk of the Hrs it con 70
tains. The vapor mixture released may contain
ammonia and hydrogen sulphide in proportion of
3-1, and a .substantial proportion oi' that quan
tity of acidic gases which was incidentally ab
sorbed with the ammonia in ß 'is thereby' re
2,106,734
While it was known that selective absorbents
moved, and is allowed to pass through pipe 43
to the top of the desulphurizer 33 to be dephleg
mated and retreated by the selective absorbent
would selectively absorb ammonia in preference
to hydrogen sulphide to a measurable extent, it
has been discovered with the present process that
substantially all of the ammonia can be sharply
separated from substantially all of the hydrogen
sulphide when present in large proportion, so
that the latter may be recovered substantially
pure, and likewise all of the ammonia separately
recovered with less contamination 'of the latterl 10I
by the former than inprior hydrogen sulphide
for removal of the ammonia, which was simul
taneously given oiî by the selective absorbent,
before the residue of acidic gases' is allowed to
pass through the outlet 38, to be put to op
tional utilization.
'
The selective absorbent passes then to the
second stage of deammoniñcation in section 42h
of the deammoniator 42, where it is given a more
vigorous treatment by direct and indirect steam,
which treatment serves'to free the selective ab
gas puriiication processes.
esses- employing ammonia as the _alkalinity for
tive absorber 35.` The selective absorbent thus
comparatively freed of ammonia, collects in the
base of the deammoniator and is then taken up
by pump 44 and delivered to heat exchanger I6
20 through pipe 45 and is then returned to the se
lective absorberv 35 through pipe 31.
,
The vapor distilled from the second stage o
the deammoniator 42h contains NH3 and HzS in
proportion of about 20-1 and` passes through
25 pipe 46 to heat exchanger 4I and thence by pipe
41 to the gas inlet ~at the base of the primary
cooler 4 tobe again recycled in the lgas and gas
liquor for use in the further removal of acidic
gases in the absorber 25.
By way of illustration, the following are given
as the types of solutions which may be employed
as selective absorbents in the process previously
described.
Such solutions may be used as are
eñective in diminishing the vapor. pressure of
35 ammonia in the -presence of acidic gases or will
raise the vapor pressure of the acidic gases as
compared with the vapor pressures of ammonia
and the acidic gases in simple '-.vater solution.
1. Solutions of ammonium salts, such as
46
a. NHiCNS
b. NH4C1
'ruega
. NHiCOzCI-Is (acetate)
. NH4H2PO4 01' (NH4) 2HPO4
45
. (NHiMSOi
Mono- or di-ammonium salts of CeHaO'z
(citric acid)
2. Solutions of sulphides, such as
Ca(HS)z
to its combining weight with the ammonia of the
gas, is 'outstanding since for the ñrst time it is
possible with the use of ammonia as the alkali
to recover from the gas in gas puriñcation over 20
ninety per cent of the hydrogen sulphide free of
ammonia with substantially complete and eco
nomical recovery of the ammonia in onel cycle of
operation.
As a speciñc example of a special’application
of this method of effectively removing ammonia
from ,admixture with acidic gases in such man
ner as to allow the ammonia to be easily and eco
nomically available for return and reuse in a
process cycle, I will cite the case in which each 30
1,000 cubic feet of coke-oven gas to which .had
been added approximately three times its nor
mal content of ammonia, upon being scrubbed
with approximately 4.5 gallons of weak ammonia
liquor yielded a fouled ‘solutioncontaining 9,000
grains of ammonia and 4,500 grains of hydrogen
sulphide. This fouled solution after heat treat
ment in the desulphurizer 33 as described above,
gave up 90% of its hydrogen sulphide content
and approximately three-fourths its ammonia.
The solution containing the unvolatilized am
monia was retu'rned to the scrubbing system and.
the gaseous mixture of ammonia and hydrogen
sulphidewas treated in the selective absorber 35
using 2.56 gallons of a solution containing 450 45
grams per‘liter of ammonium thiocyanate as the
selective absorbent. The total quantity of am
ation and approximately 75% of the hydrogen
sulphide passed out of the selective absorber 35 50
at outlet 38; the remaining 25% was absorbed
by the ammonium thiocyanate solution. In the
`
KHS
absorbing hydrogen sulphide from gas contain 15
ing the same in large proportions in comparison
monia was absorbed under the condition of oper
g. Cs`H5-SOs~NH4 .
NaHS
The efficiency, as
compared with other prior gas puriñcation proc
sorbent of a substantial amount of the remain
15 ing ammonia which was absorbed in the selec
30
3
.
-
3. Solutions of weak acids, salts of weak bases ‘ deammoniñcation of the fouled selective absorb
and strong acids, such as
ent in 42, two-thirds of that quantity of hydro
gen sulphide taken up by the ammonium thio 55
vBoric acid
55
Nitro phenols
cyanate solution was eliminated from the sys-_
NHiHnPOt-which belongs to list #1 as well. tem at 38 and one-third returned to the primary
Tri-ethanolamine chloride
`
Stearicacid either pure or dissolved in oil
4. Neutral oils
60
These various selective absorbents all raise the
vapor pressure of acidic gases like hydrogen sul
phide and carbon dioxide, but not ammonia, with
respect to ammonia andthe acidic gases in sim
65 ple water solution; and some of the aforesaid
selective absorbents also concurrently lower the
vapor pressure of ammonia: and so they all have
a greater selective amnity for ammonia of the
gas to be puriñed as compared to impurities like
70 hydrogen sulphide, carbon dioxide and the like
of the gas than mere water or weak aqueous arn
` monia gas liquor. However, they also' vary much
in effectiveness, and the preferred selective ab
sorbent is the ñrst one above-named, a solution
75 of ammonium thiocyanate.
cooler with the total ammonia which was ex
tracted from the gas in the hydrogen sulphide
absorption. Obviously, then, 92% of the hydro
60
gen sulphide originally absorbed from the un
treated gas is removed from the process in one
cycle of operation and only 8% is returned to
be extracted in the next cycle; this eiiicient re
moval of hydrogen sulphide is accompanied by 65
substantially complete» and economical recovery
of any ammonia used for the process and for this
reason the process is adaptable to a high degree
of gas puriñcation in one cycle of operation. .
- From the foregoing it appears that the gas 70
entering the primary coolers is »enriched with
gaseous ammonia from the secondary stage of
the deammoniator to theextent ofv about three
times the normal ammonia content of the gas.
After the primary cooling stage, the. gas with 75
4
,
.v aromas
its high' ratio o! ammonia to hydrogen sulphide
enters the hydrogen sulphide absorption stage
where it is scrubbed with the ammonia liquor
i'rom the primary cooling 'stage and part of the
ammoniacal liquor from the desulphurizer, a
total of ’about 4.5 gallons per MCF of about 2
to 4% concentration. 'l‘he hydrogen sulphide is
scrubbed out of the gas, leaving approximately
its normal content of ammonia; and the fouled
to l, and is there heated with about 1.0 pound ~
indirect steam and 2 pounds direct steam per
MCF gas treated. As a result of this 2.56 gallons
of selective absorbent leave the deammoniator
at about 100° C., give up part of 'their heat to
the hydrogen sulphide absorbent solution pass
ing from the hydrogen sulphide absorption stage .
to the desulphurizing stage, and then reenter the .
selective absorber where the hydrogen sulphide
liquor about 4.5 gallons per MCF` of gas treated leaves the process admixed with some CO2 at a 10
and containing about 9,000 grains NH: and 4,500 vtemperature of about 40° C. The vapors of dis
grains ,Has and some CO2, NH3, HzS and CO2
tillation leaving the secondary deammoniation
'being present in the proportions oi about'6 to 3
stage contain about 1.9 pounds steam and 6,750
to 1, is heated to about 62° C. and passes to the
15 desulphurizer where substantially all or the H28
and some CO: and free ammonia are volatilized.
grainsl NH: and 380 grains HaS per MCF gas
treated, pass in indirect heat exchange relation
with the ammonia-laden selective absorbent
passing to the prim'ary deammoniation stage,
Part of the actiiled liquor from the desulphur
izing containing residual free ammonia (about
2.5v gallons per MCF ot gas treated and-con
taining a total of 2,250 grains NH3) 'is recircuf
lated to the hydrogen sulphide absorption stage
and then are conducted to the gas in the pri
mary cooler to enrich that gas in ammonia i’or
the hydrogen sulphide absorption stage.
20
The entire sytem-is a closed cycle, wherein high
where it adds suillcient volume to the regular
concentrations of ammonia are used to remove
weak liquor from _the primary cooling stage to
provide'the required quantity of H1B scrubbing
liquor.v 'I'he remaining part (about 2.0 gallons
the hydrogen sulphide from the raw gas and the
hydrogen sulphide is later recovered by treat
ing the partially dephlegmated gases from the 25
desulphurizer with the selective absorbent. The
per MCF and containing a total oi 1,800 grains
N_Hs, its volume equalling the amount of am ’ selective absorbent by its action permits not only
escape through it of a high percentage of the
monia liquor that passes from the primary cool
-ing stage to the hydrogen sulphide absorption HzS. contained in these gases but accomplishes
stage) passes to the ammonia still wherein .all substantially complete retention of the high am 30
the free ammonia, H28 and CO: are evolved monia concentrations in the system described.
and the ?xed ammonia liberated with lime. The The'coal-gas leaving the hydrogen sulphide ab
distillation in the ammonia still requires about sorber carries the usual quantity of ammonia „
4 pounds steam per MCF of gas treated and found in gases produced by the carbonization oi
the hot vapors from the still carrying 3.7 pounds coal. consequently the normal plant yield of am 35
steam and containing about 1,800 grains' NH3 monium sulphate is not reduced and that quan
per MCF gas treated, pass into the desulphurizer
tity of ammonia used furthe. hydrogen sulphide
to drive oil the hydrogen sulphide. .These hot v removal remains entrapped in the purification
vapors leave the desulphurizer reduced in tem
perature, carrying 0.7 pound steam per4 MCF
-gas treated, and are dephlegmated together with
the toul vapors released in the deammoniator.
The vapors from the dephlegmator are bubbled
. through a strong (450 g. p. 1.)"solution of am
monium thiocyanate. This solution has a very
high absorptive capacity for ammonia and but
little ailinity for Haß at the temperature of oper-`
ation. Substantially all oi' the ammonia con
tained in the vapors is absorbed by this solution
system where it is continuously recycled.
An
advantage of the process over other ammonia hot 40
actiilcation processes lies in the very low steam
consumption, only 4.5 to 5.0 pounds per MCF
of gas treated, and virtually no chemical con
sumption. 'I‘he gases passing from the selective
absorber are a mixture of approximately 80%
H2B and 20% CO2 which is readily combustible,
and can be easily converted into sulphuric acid
to be used i'or plant requirements oi' the material.
The deammoniator is divided into two stages to
anda high percentage oi' the hydrogen sulphide take advantage oi' a fact developed in the course
is released througha vent at the top of the lof the process, that two-thirds of the hydrogen
column ladrnlxed with CO: and some water vapor. sulphide' may _be expelled in the primary stage
The ammonia-laden absorbent 'solution is fed while only a minor amount of the ammonia is
continuously at about 'l0' C. to a heat exchanger simultaneously expelled. This allows return oi’
where it is heated to about 95° C. and then . a highpercentage of the hydrogen sulphide'from 56.
the deammoniator directly to the selective ab
sorber and recirculation of nearly all of the am
enters the primary deammoniation stage where
in it is heated by about 1.5 pounds indirect steam
, per MCF gas treated.
The vapors from such
heatingleave with about 0.8 pound steam and
contain about 2,250 grains NH: and 760 grains
H2B vfor each MCF gas treated, ammonia' and
hydrogensulphideinproportionssto Landpass
ihtothe vapors entering the dephiegmation step.
monia with very little hydrogen sulphide to the ‘
raw gas in the primary cooling stage. 95% oi
the ammonia entering the selective absorberis
driven oi! in the deammoniator.
In some instances it has been found that the
ratio oi ammonia to hydrogen sulphide in the -
`,The mixed vapors from the desulphuriser and
primary deammoniation stages pass from the de
Phlegmatlng column -with .about 0.75 pound
steam and about 9,000 grains NH: and 5.260
grains HaS- per MCF gas _pur-iiied.- After heating
such'case the vapors are introduced intothe se
lective absorbent directly and after the dephleg
in the'prima‘ry deasnmoniation stage the am
mation step. that is. without dephlegmation, or
vapors leaving the. primary stage .of deammonia
tion is less than above stated, and that the vapors
may be substantially all hydrogen sulphide. In
monia-laden selective absorbent enters the sec
are introduced at a point `in the selective absorb
ondary deammoniation stage at about l100°:C.,` ' ent step where the NH: and H18 relationship in
containing about 2.680 grains NH: and '150 grains
Has per gallon o! selective absorbent, the am
monia and hydrogen sulphide. in proportion 20
the vapors o! such step is similar to that oi' the
vapors issuing trom the primary stage of`de
ammoniation.
^
.
'Il
2, 106,784
In the example above given the dephlegmation
and selective absorbent stage are operated so
that the vapors after dephlegmation and the solu
tion in the selective absorbent stage have a tem
perature of about '70° C. However, it has been
found advantageous to have the temperature of
the vapors after the dephlegmation step and the
solution in the selective absorbent stage not below
about 50° C. In either case the vapors leave
the selective absorbent stage at not over 40° C.
which may be obtained by cooling coils inside the
scrubber sections if necessary.
Lower temperatures than about 50° C. in the
selective absorbent solution and in the vapors
15 after the dephlegmation step are not preferred
because at 'still lower temperatures there would
be failure of the preferential absorption actio‘n
by which nearly all of the ammonia is absorbed
vbut almost none of the hydrogen sulphide, and
also there is avoidance of a tendency for de
posists of ammonium carbonates and sulphides
which might plug the equipment.
‘
It further appears that the stronger the selec
tive absorbent solution, the more selective will be
the absorption. Consequently, 'it is desirable that
a salt of high solubility be used, and one that. is
not salted out when the solution, absorbs am
monia. The salts NH4CNS, NHrCl, and the cit
rate appear to be the most desirable; and of those
NHiCNS is particularly so, since this selective
absorbent will be especially eiîective and vwill be
formed during the operation of the process and
5
f
liquor containing the remaining part ci the am
monia to the scrubbing step; partially dephleg
mating the so expelled hydrogen sulphide and
admixture of ammonia and scrubbing theA said
gaseous mixture with a concentrated selective ab
sorbent solution of an ammonia absorbent effec
' tive to raise the vapor pressure of hydrogen sul
phide as compared with the vapor pressure of
ammonia and hydrogen sulphide in simple water
solution, in continuous ñow into and out of con
tact with said gaseous mixture of hydrogen sul
phide and ammonia without admixture of the
selective absorbent solution with the coal gas
scrubbing liquor', to eiîect a preferential absorp
tien-tof the ammonia from the mixture, the de 15
phlegmating being so limited that at the result
ing moderately reduced temperature said ab
sorbent solution absorbs only a minor portion of
the said hydrogen sulphide while preferentially
absorbing substantially all of the residual am 20
monia from _the mixture; releasing the unab
sorbed hydrogen sulphide; continuously discharg
ing and regenerating the selective absorbent solu
tion separately from the expelling of the hydro
gen sulphide from the fouled coal-gas scrubbing
liquor by reheating and distilling to remove the
residual absorbed hydrogen sulphide and the ab
sorbed ammonia; returning the ammonia as ex
cess to fortify the gas scrubbing liquor by recir
culating the so removed constituents through the
rrior scrubbing steps; and recirculating said
regenerated absorbent solution.
2. A process for recovery of hydrogen lsulphide
accumulate in the selective absorbent solution «in
suilìcient quantities to compensate for any nor' from coal-gas, comprising: absorbing the hy
mal mechanical losses in operation. The actual drogen sulphide by scrubbing the coal-gas with
production of the selective absorbent used in the' ' its own ammoniaca] liquor fortified with am
process incidental to its operation therefore' re-A monia to an extent greatly in excess of the nor
sults in a financial advantage'by avoiding any
monetary outlay for the necessary reagent.
The process removes some carbon dioxide from
the gas. It has been found possible to operate
the system for H2S recovery in the presence of
considerable amounts of carbon dioxide. This
is because HzS is absorbed much more rapidly
from gas than is CO2. 'I‘he gas scrubbing step
can be accordingly designed and operated so that
it is just efficient enough to remove the desired
amount 'of HzS, under which lconditions the
amount of CO2 absorbed will be small.` But when
it is desired to operate for CO2 removal or
recoveryl from gas, it is merely necessary to make
the gas scrubbing step of suificient capacity to
remove the desired amount of CO2. The selective
absorbents would be the same as those listed
mal ammonia content oi such liquor, the excess
>being maintained by recirculation of ammonia
from a further stage in the treatment system;
expelling the hydrogen sulphide and part of the
ammonia `from the fouled scrubbing liquor by hot
vapors from the distilling of ammonia from part
of said liquor and returning the scrubbing liquor
containing the remaining part of the ammonia 45
to the scrubbing step; partially cooling the so
expelled hydrogen sulphide and admixture of
ammonia and scrubbing the said gaseous mixture
with a concentrated selective absorbent solution
of ammonium thiocyanate in continuous ilow into
and out of contact with said gaseous mixture of
hydrogen sulphide and ammonia without ad
mixture of the selective absorbent solution -with
the coal-gas scrubbing liquor to eiîect a pref
erential absorption> of the ammonia from the
mixture, the partial cooling being so limited that
55 above with the exception of list #2. Solutions
of carbonates (as NazCOs and K2CO3) are also
selective absorbents for the process for CO2 re ` at the resulting temperature said absorbent solu
moval.
Y
The invention as hereinabove set forth is em
tion absorbs only a minor portion of the said hy
drogen sulphide while preferentially absorbing
bodied in particular form and manner but may
be variously embodied within the scope of the
claims hereinafter made.
substantially all o! the residual ammonia from
monia to an extent greatly in excess' of the nor
mal ammonia content of such liquor, the excess
returning the ammonia as excess to fortify the
gas scrubbing liquor-.by recirculating the so re
.the mixture; releasing the unabsorbed hydrogen
sulphide; continuously discharging and regen
erating the selective absorbent solution separately
I claim:
1. A process for recovery of hydrogen sulphide from the expelling of the hydrogen sulphide from
the fouled coal-gas scrubbing liquor by reheating
from coal-gas, comprising: absorbing the hy
drogen sulphide by scrubbing the coal-gas with and distilling tov remove the residual absorbed
hydrogen sulphide and the absorbed ammonia;
its own ammoniacal liquor fortified with am
70 being 'maintained by recirculation of ammonia
from a further stage in the treatment system;
expelling the hydrogen sulphide and part of the
ammo-nia fromdthe fouled scrubbing liquor by
hot vapors from `the distilling of ammonia from
75 part of said liquor and returning the scrubbing
moved constituents through the prior scrubbing 70
steps; and recirculating said'regenerated‘ ab
sorbent solution.
-
3. A process for removal of acidic gases from
coal-gas, comprising: absorbingffft-he acidic gases
like ms, CO2, and HCN by scrubbing the coal
2,106,7s'4
gasA with its own ammoniacal liquor fortined
through the prior scrubbing steps; and recirculat
with ammonia to an extent greatly in excess of
ing said regenerated absorbent solution.
the normal ammonia content of such liquor, the
excess being maintained by recirculation of am
B_Aprocessforseparatingamixtureof am
monia and such weakly acidic compounds as
hydrogen sulphide. hydrogen cyanide or carbon
monia from a further stage in the treatment sys
tem; expelling the> acidic gases and part ofthe ` dioxide in aqueous solution into their chemical
ammonia from the fouled scrubbing liquor by classes> comprising: distilling the- aqueous vsolu
hot vapors from the distilling of ammonia from tion, dephlegmating the -vapors of distillation,
part of said liquor; partially dephlegmating the then scrubbing the vapors with' a selective ab
so expelled acidic gases and admixture of am»
monia and scrubbingthe ysaid gaseous mixture
» with a concentrated selective absorbent solution`
of a salt effective to absorb ammonia and concur
rently raise the vapor pressure of the acidic gases
as compared with the vapor pressure of ammonia
sorbent of an ammonia absorbent effective to
raise the vapor pressure of the acidic gases as
compared with the vapor pressure of ammonia
and the acidic gases in simple water'solution, dis- ' `
charging and regenerating the selective absorbent
subsequently by distillation in separately con 115>
and the acidic gases in simple;water solution, in v trolled primary and secondary concurrent succes
continuous flow into and out of contact with said sive stages in the nrst of which the selective ab
gaseous mixture of acidic gases and ammonia sorbentisheatedtoexpelmostoftheacidicgases
but relatively little of the ammonia and in thewithout admixture of the selective absorbent so
lution with the coal gas scrubbing liquor, to eifect second of which the selective absorbent is sub-`
a preferential absorption of the ammonia from jected to higher heating to remove most of the
the mixture. the dephlegmoting being so limited absorbed ammonia, and in which the unvaporiaed
residue of the spent selective absorbent flows from
that at the resulting moderately reduced tem
perature said absorbent solution absorbs only a the first to the second stages during the regenera
reduced portion of the said acidic gases while tion in each stage, and in which the vapors of dis- l
preferentially absorbing substantially all of the tillation are yseparately withdrawn from the re]
residual ammonia from the mixture:- releasing
the unabsorbed acidic gases: continuously dis
charging and regenerating. the selective absorbent
solution separately from the) expelling of the
acidic gases‘from the fouled coal-'gas scrubbing
liquorbyreheatinganddistiliingtoremovethe
spective stages; and returning the regenerated
selective absorbent to the selective absorbent
stage and the vapors of distillation from tliepri
mary stage of regeneration to the aforesaid
dephlegmation stage.
~
v
6.Aprocessforseparatingamix_tureofam-
residual abmrbed acidic gases and the absorbed
monia and acidic gases comprising: scrubbing
ammonia; returning the ammonia as excess to
the mixture with a selective absorbent of a" salt
fortify the gas scrubbing liquor by recirculating
effective to absorb ammonia and concurrently 351.
materially increase the vapor pressure of the
_ the so removed constituents through the prior
scrubbing steps; and recirculating said regener
> ated absorbent solution.
«
4. A process for removal of acidic gases from
acidic gases above that exhibited by them in sim
ple aqueous solutions. of them and ammonia, dis
charging and regenerating the selective absorbent
coal-gas. comprising: an absorption stage , in
subsequently by’distillation in separately con
which the acidic gases are absorbed by 'scrubbing
trolled primary and secondary concurrent succes
sive stages in the i‘irst of which the selective ab
sorbentis heated to expelmost of the acidic gases
coal-gas with ammonia liquor by recirculation of
ammonia from a further stage in the treatment,
and an actiiication stage comprising the steps of
expelling the acidic gases and part of the’ am
monia from the fouled-scrubbing liquor by heat
and returning the scrubbing liquor containing the
remaining part of the ammonia to the scrubbing
step, partially dephlegmating the so expelled
acidic gases and admixture of ammonia and
scrubbing the said gaseous mixture with a con~
centrated selective absorbent solution of an am
monia absorbent eñective’to raise the vapor pres
sure of the acidic gases as compared with the
vapor pressure of ammonia and the acidic gases
in simple water solution, in continuous iiow into
and out f‘f contact with said gaseous mixture`of
acidic gases and ammonia without admixture of
the selective absorbent solution with the coal-gas
scrubbing liquor, to eifect a preferential absorp
tion of the ammonia from the mixture, the de
phlegmating being so limited that at the resulting
moderately reduced temperature said absorbent
solution absorbs only a reduced portion of the said
acidic gases while preferentially absorbing sub
stantially all of the residual ammonia from the
mixture, releasing the unabsorbed acidic gases.
regenerating the selective absorbent solution sepa
rately from the expelling ofthe acidic gases from
the fouled coal gas scrubbing liquor by reheating
land distilling to remove the residual absorbed
acidic gases and the absorbed ammonia; returning
the ammonia as excess ‘to fortify the gas scrubbing
lns liquor by recircuiating the so removed constituents
but relatively little of the ammonia and in the
second of which the selective absorbent is sub
Jected tohigher heating to remove most of the
absorbed ammonia. and in which the unvaporized
residue of the spent selective absorbent flows from
the ñrst to the second stages during the regenera
tion in each stage, and in which the vapors of
distillation are separately withdrawn from the
respective stages; and returning the regenerated
selective absorbent to the selective absorbent
stage.
,
_
7. A process of removing hydrogen sulphide
from gases containing it. comprising: continuously '
recirculating an aqueous liquid through a gas
washing cycle in which the gas is washed in an l
absorption stage in the presence of suilicient am
monia to' remove the hydrogen sulphide there
from forming a solution capable of giving up
ammonia and hydrogen sulphide upon heating,
andl through an actifying stage in ,which the
fouled solution- is actiiied by heating to drive off
the absorbed hydrogen sulphide; treating the va
pors from the actiiication stage with a selective
absorbent solution of a salteifective to absorb
ammonia and concurrently,raise the vapor pres
sure of the acidic gasesas compared with the
vapor pressure of ammonia" and the acidic gases in
simple water solution and thereby selectively ala--`
sorbing the ammonia from said vapors; regener
ating the selective absorbent by preliminary con
trolled heating just sui'iicient to drive on hydrogen
sulphide but not much ammonia thereinl and sec 75
7
ondary separately controlled heating to remove
substantially the balance of ammonia and hy
‘ drogen sulphide; returning the vapors from the
primary heating to the vapors given oiI during
the actiilcation and the vapors from the secondary
>heating to the gas ¿tobe purified to enrich it in
ammonia for hydrogen sulphide absorption.
8. A 'process of purifying gas of hydrogen sul
phide, comprising -washing gas‘ containing am
monia and hydrogen sulphide in a hydrogen sul
phide absorption stage with an ammoniaca] ab
sorbent solution to leave a predetermined am
monia content in the gas but-to concurrently re
, move the hydrogen sulphide therefrom forming
circulating the deammoniated selective absorb
ent from the _deammoniating step back to the
selective absorption step.
^ l0. A process for the recovery of hydrogen sul
phide from coal-gas, comprising: primary cool
ing of the gas. while hot from` its generation;
absorbing the hydrogen sulphide by scrubbing
the _coal-gas with ammoniacal liquor from the
primary cooling stage fortified with recirculated
ammonia liquor to any extent to remove the _hy 10
drogen sulphide from the gas but leave therein
ammonia initially in the gas, desulphurizing the '
fouled liquor by expelling the hydrogen sulphide
and part of the ammonia from the fouled scrub
ammoniacal salts with the hydrogen sulphide bing liquor by hot vapors; recirculating part of
the liquor from the desulphurizing step 4to the
capable of giving up hydrogen sulphide and am
monia upon heating; desulphurizing the fouled _gas scrubbing step and distilling the remaining
absorbent solution by heating to drive oif most of part to liberate residual free ammonia and ñxed
the absorbed hydrogen sulphide; recirculating ammonia as hot vapors; passing the hot vapors
part of the desulphurized absorbent solution to \from the distilling step while containing the free
the hydrogen sulphide absorption stage and dis-- ammonia therefrom through the desulphurizing
tilling the remaining part to volatilize remaining step to effect the desulphurizing therein; par
tially dephlegmating the mixture of hot vapors
ammonia and hydrogen sulphide Y therefrom;
effecting the heating of the desulphurizing s‘ep containing the expelled hydrogen sulphide and
admixture of ammonia from the desulphurizing
with the hot vapors from the distilling step; de
phlegmating the last named vapors together with step and scrubbing the mixture with a. `selective
the vapors driven off in the desulphurization step absorbent solution of an ammonia absorbent ef
and then washing the same with a selective ab
sorbent oi’ an ammonia absorbent eñective to
raise the vapor pressure of the acidic gases as
compared with the vapor pressure of ammonia
and the acidic gases in simple water solution;
deammoniating the ammonia-laden selective ab
sorbent in a separate stage by separately con
trolled less vigorous primary and more vigorous
Vsecondary heating; conducting the deammonia
tion vapors from the primary heating to the de
phlegmation step and the vapors from the sec
ondary heating into the gas to enrich it in am
monia for the hydrogen sulphide absorption step;
and recirculating the deammoniated selective ab
sorbent from the deammoniating step back to the
selective absorption step.
-
fective to raise the vapor pressure of the acidic
gases as compared with the vapor pressure of
ammonia and the acidic gases in simple water
solution, the dephlegmating being so limited that
at the resulting moderately reduced temperature
said absorbent solution absorbs only a minor
portion of the hydrogen sulphide while'prefer
entially absorbing substantially'all of the residual
ammonia from the mixture; releasing the unab
sorbed hydrogen sulphide; regenerating the se
lective absorbent solution by reheating and dis
tilling to remove the residual hydrogen sulphide
and the absorbed ammonia in separately con
trolled less vigorous primary and more vigorous
secondary stages; returning the vapors from the
primary stage to the system ahead of the selec
tive absorbent stage; returning the vapors from
_the secondary stage to the coal-gas in the pri
9. A process of purifying gas of hydrogen sul
phide, comprising: washing gas containing am
monia and hydrogen sulphide in a hydrogen sul f mary cooling stage; and recirculating the regen
erated selective absorbent to the selective absorb
phide absorption stage with an ammoniacal ab
'
sorbent solution to remove the hydrogen sulphide ent stage.
l1. A process for the recovery of hydrogen sul
therefrom forming ammonia/cal salts with the phide
from coal-gas, comprising: primary cool 50
hydrogen sulphide capable of giving up hydrogen
ing
of
the gas while hot from its generation;
sulphide and ammonia upon heating; desulphur
the hydrogen sulphide by scrubbing the
izing the fouled absorbent solution by heating absorbing
coal-gas with ammoniaca] liquor from the pri
to drive off most of the absorbed hydrogen sul
phide; recirculating part of the desulphurized mary cooling stage fortiñed with recirculated
absorbent solution to the hydrogen sulphide ab
sorption stage and distilling the remaining part
to volatilize remaining ammonia and hydrogen
sulphide therefrom; effecting the heating _of the
-desulphurizing step with the hot vapors from
00 the distilling step; dephlegmating the last named
vapors together with the vapors driven oil~ in
the desulphurization step and then washing the
same with a selective absorbent of a salt effec
tive to absorb ammonia and concurrently raise
ammonia liquor to an extent to remove the hy
drogen sulphide from the gas but leave therein
ammonia initially in, the gas, desulphurizing the
foul liquor by expelling the hydrogen sulphide
and part of the ammonia from the fouled scrub
bing liquor by hot vapors; recirculating part of
the liquor from the desulphurizing step to the gas
scrubbing step and distilling the remaining part
to liberate residual free ammonia and fixed am
monia as hot vapors; passing the hot vapors from
the distilling step while containingthe free am
the vapor pressure of the acidic gases as com
pared with »the vapor pressure of ammonia and ' monia therefrom through the desulphurizing step
the acidicA gases in simple water solution; deam
moniating the ammonia-laden selective absorb
ent in a separate 'stage by separately controlled
- less vigorous primary and more vigorous second
ary heating; conducting the deammoniation va
pors from the primary heating to the dephlegma
tion step and the vapors from the secondary heat
ing into the gas to enrich it in ammonia for
the hydrogen sulphide absorption step; and re
to eifect the desulphurizing therein; partially de
phlegmating the mixture of hot vapors contain
ing thevexpelled hydrogen sulphide and admix
ture of ammonia from the .desulphurizing step 70
and scrubbing the mixture with a selective ab
sorbent solution of a salt eiîective to absorb am
monia and concurrently raise the vapor pressure
of the acidic gases as compared with the vapor
pressure of ammonia and the acidic gases in sim 75
8 .
amava
ple >water solution, the dephlegm'ating being so
limited that at the resulting moderately reduced
reduced temperature at which said absorbent
solution absorbs only a minor portion of the said
temperature said absorbent solution absorbs only
hydrogen sulphide while preferentially absorbing
a minor portion of the hydrogen sulphide while . substantially all of the residual ammonia from
_ I .preferentially absorbing substantially all of the the mixture; releasing the unabsorbed hydrogen 6
residual ammonia from the mixture; releasing sulphide; regenerating the selective absorbent, so
the unabsorbed hydrogen sulphide; regenerating lution by reheating and distilling to remove the
the selective absorbent` solution by reheating and residual absorbed hydrogen sulphide and the ab
>distilling to remove~ the residual hydrogen sul
sorbed ammonia; returning the'ammonia as ex
10 phide and the absorbed ammonia in separately cess to fortify the gas scrubbing liquor by recir- lo
controlled less vigorous primary and more vigor >culating the so removed constituents through the
ous secondary stages; returning the vapors from prior scrubbing steps; and recircuiating said re
the primary stage to the dephlegmating step be
generated absorbent solution.
tween the desulphurixing stepand the selective
l4. A process for the recovery of hydrogen >sul
1s absorbent stage; returning the vapors from the ~ phide imm coal-gas, comprising: primary cooling 1l
f secondary stage to the coal-gas in the primary' of the gas while hot from its generation; absorb
cooling stage; and recircuiating the regenerated
selective absorbent to the selective absorbent
stage.
ao-
12; A process for removal of acidic gases from
coal-gas, comprising: absorbing the acidic gases
by scrubbing the coal-gas with its own’ammo
ing the hydrogen sulphide by scrubbing the coal
gas with ammoniacal liquor from the'primary
cooling stage forti?ed with recirculated ammonia ~
liquor to an extent to remove the hydrogen sul- 80
phide from the gas but leave. therein ammoniav
initially in the gas, desulphurlsing the fouled
niacal liquor fortiiled with ammonia to an extent - liquor by expelling the hydrogensulphide and
greatly in excess of the normal ammonia content part ofthe ammonia from the fouled scrubbing
Il of such liquor, the'exeess being maintained _by
recirculation of ammonia from a further stage
' in the treatment system; expelling the acidic
liquor byvhot vapors; recirculating part of Athe 'I
liquor from the desulphuridng step to the gas
scrubbing step and distilling'the remaining part.
gases and >pari: of the ammonia from the lfouled ' to _liberate residual free ammonia and ilxedam- scrubbing liquor by hot vapors fromy the distil
monia as hot vapors; passing the' hot .vapors
80 ling of ammonia from part of said liquor and throughthedesulphuriaingst'eptoedecttbede-v“
returning the scrubbing liquor containing _the
remaining part of the ammonia to the scrub
bing step: partially dephlegmating the so ex
pelled acidicgases and admixture of ammonia
as l,and scrubbing the mixture with a selective ab»`
sorbent solution of an ammonia absorbent eifec
tive to raise >the vapor pressure „of the acidic
sulphurizing therein; partialb depblegmating the
mixture of ho_t vapors containing the expelled
hydrogen sulphide and `admixtm'e of’ ammonia
from the desulphurizlng step 4and scrubbing the f
mixture with a selective absorbent solution that 8l
eil’ects a preferential
of the ammonia.
the d_ephlegmating being so limited that at the
gases as compared with~ the vapor pressure of resulting moderately reduced temperature said
ammonia and the acidicgases in simple water ` absorbent solution absorbs only‘ a'minor portion
4,0 solution, the dephlegmating beingl so limited that of the hydrogen sulphide while preferentially ab- ‘a
at the resulting moderately reduced temperature sorbing. substantially all of the residual‘_.ammo-- ._
said absorbent solution absorbs only a reduced nia from the mixture: releasing the unabsorbed`
portion-of the said acidic gases while prefer
hydrogen sulphide; regenerating‘the selective ab-.'
entially absorbing substantially all of the resid
sorbent solution by reheating and distilling> to '
a ual ammonia fromwtbe mixture; releasing the remove the residual hydrogen sulphide and the 45
unabsorbed acidic gases from contact with the absorbed ammonia in primary and secondary
selective absorbent at a temperature of approxi
stages: returning the vapors from the primary
mately 40° C.; regenerating the selective absorb stage to the system at a sone in the selective ab
»
ent solution by reheating and distilling to remove sorbent stage where the NH; and Has relationship
‘o the residual absorbed acidic gases and the ab
'
sorbed ammonia; returning the ammonia as ex
cess to fortify the gas scrubbing liquor by recir
culating the so removed constituents through the
, prior scrubbing steps; and recirculating said
55 regenerated absorbent solution.
13. A process for recovery of hydrogen sulphide
from coal-gas, comprising: absorbing the hydro
gen sulphide by scrubbing .the coal-gas with its
own- ammoniacal liquor _forti?ed with ammonia
>ß() to an extent -greatly in excess of the normal am
monia content of such liquor, the excess being
maintained by recirculation of ammonia from a
further stage in the treatment system; expelling
the hydrogen sulphide and part of the ammonia
g5 from the fouled scrubbing liquor by hot vapors
from the distilling of ammonia from part of said
liquor and returning the scrubbing liquor con
taining the remaining part of the ammonia to the
scrubbing step: scrubbing the _mixture with a
l 70 selective absorbent solution of a salt effective to
in the vapors in such stage is similar tothat oi u
the vapors issuing from said primary stage;- re
turning the vapors from the secondary stage to
the coal-gas inthe primary cooling stage;- and re
circulating the regenerated selective absorbent to
the selective absorbent stage.
‘ f ß
15. A process for the recovery of hydrogen
sulphide from coal-gas, comprising:
v
primary -
cooling of the gas while hot from- its generation;
absorbing the hydrogen sulphide by scrubbing
the coal-gas with ammoniacal liquor from the .œv
primary cooling stage fortified with recirculated
ammonia liquor to an extent to remove- the hy.
drogen sulphide from the gas but leave therein \
ammonia initially in the gas, desulphurising the
fouled liquor by expelling the hydrogen sulphide ß
and part of the ammonia from the fouled scrub
bing liquor by hot vapors; recirculating part oi'
the liquor from the desulphurizing step to the gas
scrubbing step and distilling the remaining part
to liberate residual free _ammonia-andi‘ixed am- 1o
absorb ammonia and concurrently‘raise the vapor monia as hot vapors; passing the hot vapors
pressure -of the acidic gases as compared with through the desulphurizing step to eifect the de-'
the vapor pressure of ammonia and the acidic sulphurizlng therein; partially dephlegmating the
gases in simple water solution to eifect a prefer
mixture of hot vapors containing'the expelled hy
” ential absorption of the ammonia at a moderately drogen sulphide and admixture of ammonia from u"
i
9
2,106,734
the desulphurizing step and scrubbing the .mix
ture with a selective absorbent solution, of an
ammonia absorbent effective to raise the vapor
pressure of the acidic gases as compared with the
Ll vapor pressure of ammonia and the acidic gases-
in simple water solution, the dephlegmating be
. phideïnregenerating the selective absorbent solu
Vtion by reheating and distilling to remove the
' residual hydrogen sulphide and the absorbed am
monia in primary and secondary stages; return
ing the vapors from the primary stage to the sys- Y
sulphide while preferentially absorbing substan
tem after the dephlegmation step and directly to
the solution of the selective absorbent stage; re
turning the vapors from the secondary stage to>
the coal-gas in the primary cooling stage; and
recirculating the regenerated selective absorbent 10
tially all of the -residual ammonia from the mix
to the selective absorbent stage.
ing so limited that at the resulting moderately re
duced temperature said absorbent solution ab
sorbs only a minor portion' of- the' hydrogen
ture; releasing the unabsorbed hydrogen sul
f
,
HERBERT A. GOLLMAR.
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